This invention relates to methods and apparatus for cleaning systems, and more particularly to methods and apparatus for carbon dioxide dry cleaning systems having multiple wash tanks.
Organic solvents such as perchloroethylene and other low-pressure liquid solvents have long been popular for use in cleaning systems such as dry cleaning systems. Recently, however, there are growing concerns that these solvents may harm the environment and pose occupational safety hazards. These concerns have led to an extensive search for alternative solvents that are less hazardous and systems for applying such solvents.
Some of this research has focused on systems utilizing solvents that are gases at low pressure. These systems may operate either under subcritical conditions such that the solvent is present as a liquid or under supercritical conditions such that the solvent is present as a supercritical fluid. Some of these systems utilize liquid carbon dioxide (CO2) as a cleaning solvent.
PCT Publication WO 99/13148 to Shore et al. describes a cleaning system using liquid CO2. Shore describes evacuating a cleaning chamber to remove air from the chamber. Shore also discusses filling the chamber with carbon dioxide gas from either a distillation vessel or a liquid CO2 storage tank as part of a prefill mode. Shore further describes how draining liquid carbon dioxide from the cleaning chamber leaves carbon dioxide gas in the chamber and discusses an apparatus for reclaiming this gas using a compressor and a condenser to return reliquified CO2 to a liquid storage tank.
The system described by Shore is inefficient making it expensive to operate and expensive to construct. For example, filling the cleaning chamber with CO2 gas from a distillation vessel requires that a distillation vessel be supplied and operated. Alternatively, using vaporization of the liquid CO2 in the storage tank requires the storage tank to contain a heater sized to provide make-up heat equal to the heat of vaporization of the liquid CO2 that is converted to vapor.
Furthermore, a condenser must be supplied which is sized to handle the extreme vapor loads experienced at the beginning of the vapor reclamation operation. Additionally, cooling must be supplied to this condenser. Other methods for removing the CO2 gas from the cleaning chamber such as venting to atmosphere, which results in loss of CO2 from the system, or sparging as described in PCT Publication WO 97/33031 to Taricco are similarly inefficient.
A small amount of air in the system may be beneficial, providing a partial pressure in the liquid CO2 storage tank and resulting in increased net positive suction head for the pump. However, the efficiency of the condenser can be drastically affected by even small amounts of air. Thus, a vacuum pump must be operated before each cycle to ensure that all air has been evacuated from the cleaning chamber.
Further inefficiencies occur in carbon dioxide cleaning systems that employ cleaning solutions comprising liquid carbon dioxide and other additives or detergents. To create a source of liquid CO2, these systems rely on evaporators or stills to separate additives and contaminants from the cleaning solution and generate CO2 vapor. Such stills and evaporators require heating elements, which must be sized to supply sufficient CO2 vapor and operated using steam or electricity.
The present invention provides a cleaning apparatus having multiple wash tanks for washing articles in a carbon dioxide dry cleaning system employing a liquid carbon dioxide cleaning solution. Cleaning apparatus having multiple wash tanks of the present invention may improve the thermodynamic efficiency of a liquid carbon dioxide dry cleaning system by allowing carbon dioxide vapor to be transferred between wash tanks rather than being condensed. Cleaning apparatus having multiple wash tanks of the present invention may share one or more components between the multiple wash tanks. For example, cleaning apparatus having multiple wash tanks of the present invention may have only one pump, one compressor, one working tank, one condenser, one control cabinet, one chiller, one soap injection system, one distillation system, and one vacuum system while providing the washing capacity of multiple cleaning systems each having a single wash tank. Thus, cleaning apparatus having multiple wash tanks of the present invention may have a lower capital cost than several single wash tank apparatus that do not share one or more components.
Cleaning apparatus of the present invention having multiple wash tanks for washing articles in a carbon dioxide dry cleaning system employing a liquid carbon dioxide cleaning solution include a first wash tank for contacting a first article with liquid carbon dioxide cleaning solution, and a second wash tank for contacting a second article with liquid carbon dioxide cleaning solution. The second wash tank is in fluid communication with the first wash tank.
In embodiments of the present invention, the apparatus may include a working tank for storing liquid carbon dioxide cleaning solution. The working tank may be in fluid communication with at least one of the first wash tank and the second wash tank. The apparatus may include a first piping system that provides liquid communication between the first wash tank, the second wash tank, and the working tank. The apparatus may include a pump for transferring liquid carbon dioxide cleaning solution between the first wash tank, the second wash tank, and the working tank. The pump may reside in the first piping system. The apparatus may include a second piping system that provides vapor communication between the first wash tank and the second wash tank. The apparatus may include a compressor for transferring carbon dioxide vapor between the first wash tank and the second wash tank. The compressor may reside in the second piping system. The apparatus may include a condenser for condensing carbon dioxide vapor to liquid carbon dioxide. The condenser may be in fluid communication with the first wash tank, the second wash tank and the working tank.
In still other embodiments, the apparatus may include a vapor tank for storing carbon dioxide vapor. The vapor tank may be in fluid communication with at least one of the first wash tank and the second wash tank. The apparatus may include a first piping system that provides vapor communication between the first wash tank, the second wash tank, and the vapor tank. The apparatus may include a compressor for transferring carbon dioxide vapor between the first wash tank, the second wash tank, and the vapor tank. The compressor may reside in the first piping system. The apparatus may include a second piping system that provides liquid communication between the first wash tank and the second wash tank. The apparatus may include a pump for transferring liquid carbon dioxide cleaning solution between the first wash tank and the second wash tank. The pump may reside in the second piping system. The apparatus may include a condenser for condensing carbon dioxide vapor to liquid carbon dioxide. The condenser may be in fluid communication with the first wash tank, the second wash tank, and the vapor tank.
In yet other embodiments, the apparatus may include a third wash tank for contacting a third article with liquid carbon dioxide cleaning solution. The third wash tank may be in fluid communication with at least one of the first wash tank and the second wash tank. The apparatus may include a first piping system that provides vapor communication between the first wash tank, the second wash tank, and the third wash tank. The apparatus may include a compressor for transferring carbon dioxide vapor between the first wash tank, the second wash tank, and the third wash tank. The compressor may reside in the first piping system. The apparatus may include a second piping system that provides liquid communication between the first wash tank, the second wash tank, and the third wash tank. The apparatus may include a pump for transferring liquid cleaning solution between the first wash tank, the second wash tank, and the third wash tank. The pump may reside in the second piping system.
According to the present invention, methods of washing articles using a carbon dioxide dry cleaning system employing a liquid carbon dioxide dry cleaning solution include removing carbon dioxide vapor from a first wash tank, and charging at least a portion of the carbon dioxide vapor into a second wash tank.
In embodiments of the present invention, the method may include transferring liquid carbon dioxide cleaning solution from a working tank to the second wash tank, washing a first article in the second wash tank, and transferring liquid carbon dioxide cleaning solution from the second wash tank to the working tank. The operation of charging at least a portion of the carbon dioxide vapor into a second wash tank may precede the operation of transferring liquid carbon dioxide cleaning solution from a working tank to the second wash tank. The method may include unloading a first washed article from the first wash tank, and loading a second article into the first wash tank. The operation of removing carbon dioxide vapor from the first wash tank may precede the operation of unloading a first washed article from the first wash tank. The operations of unloading a first washed article from the first wash tank and loading a second article in the first wash tank may occur during one or more of the operations of transferring liquid carbon dioxide cleaning solution from a working tank to the second wash tank, washing a first article in the second wash tank, and transferring liquid carbon dioxide cleaning solution from the first wash tank to the working tank.
In still other embodiments of the present invention, the operations of removing carbon dioxide vapor from a first wash tank and charging at least a portion of the carbon dioxide vapor into a second wash tank may include transferring carbon dioxide vapor from the first wash tank having a higher pressure to the second wash tank having a lower pressure utilizing a piping system, pumping the carbon dioxide vapor out of the first wash tank using a compressor when the differential pressure between the first wash tank and the second wash tank is less than about 100 psig, condensing a portion of the carbon dioxide vapor into liquid carbon dioxide in a condenser, storing the liquid carbon dioxide in a working tank, and stopping the compressor when the pressure in the wash tank is less than about 100 psig. The operation of removing carbon dioxide vapor from the first wash tank may include venting carbon dioxide from the first wash tank to atmosphere.
In yet other embodiments of the present invention, the method includes removing carbon dioxide vapor from the second wash tank, and charging at least a portion of the carbon dioxide vapor into the first wash tank. The operation of transferring liquid carbon dioxide cleaning solution from the second wash tank to the working tank may precede the removing of carbon dioxide vapor from the second wash tank.
According to the present invention, methods of washing articles using a carbon dioxide dry cleaning system employing a liquid carbon dioxide dry cleaning solution include transferring liquid carbon dioxide cleaning solution from a first wash tank to a second wash tank, removing carbon dioxide vapor from the first wash tank to a vapor tank, storing the carbon dioxide vapor in the vapor tank, and charging the first wash tank with carbon dioxide vapor from the vapor tank.
In embodiments of the present invention, the method may include washing a first article in the second wash tank. At least a portion of the operation of washing a first article in the second wash tank may occur during one or more of the operations of removing carbon dioxide vapor from the first wash tank to a vapor tank, storing the carbon dioxide vapor in the vapor tank, and charging the first wash tank with carbon dioxide vapor from the vapor tank.
In other embodiments of the present invention, the method may include unloading a first washed article from the first wash tank, and loading a second article into the first wash tank. The operations of unloading a first washed article from the first wash tank and loading a second article into the first wash tank may occur during the operation of storing the carbon dioxide vapor in the vapor tank.
In still other embodiments, the method may include transferring liquid carbon dioxide from the second wash tank to the first wash tank, removing carbon dioxide vapor from the second wash tank to the vapor tank, storing the carbon dioxide vapor in the vapor tank, and charging the second wash tank with carbon dioxide vapor from the vapor tank. The operation of charging the second wash tank with carbon dioxide vapor from the vapor tank may precede the operation of transferring liquid carbon dioxide cleaning solution from the second wash tank to the first wash tank.
According to the present invention, methods of washing articles using a carbon dioxide dry cleaning system employing a liquid carbon dioxide cleaning solution include transferring liquid carbon dioxide cleaning solution from a first wash tank to a second wash tank, removing carbon dioxide vapor from the first wash tank, and charging at least a portion of the carbon dioxide vapor into a third wash tank.
In embodiments of the present invention, the method may include washing a first article in the second wash tank. The method may include transferring liquid carbon dioxide cleaning solution from the first wash tank to the third wash tank, removing carbon dioxide vapor from the second wash tank, and charging at least a portion of the carbon dioxide vapor removed from the second wash tank into the first wash tank. The operation of washing a first article in the second wash tank may precede the transferring of liquid carbon dioxide cleaning solution from the second wash tank to the third wash tank.
In other embodiments of the present invention, the method may include washing a second article in the third wash tank, transferring liquid carbon dioxide cleaning solution from the third wash tank to the first wash tank, removing carbon dioxide vapor from the third wash tank, and charging at least a portion of the carbon dioxide vapor into the second wash tank.
According to other embodiments of the present invention, coating apparatus having multiple coating tanks and methods of using such apparatus are also provided.
Methods and apparatus according to the present invention may therefore improve the thermodynamic efficiency of and reduce the capital costs associated with liquid carbon dioxide dry cleaning systems. It will be understood that the present invention may be embodied as methods and apparatus and combinations thereof.